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When a Boston firefighter can't make his shift, a colleague steps in, on condition the favor will be returned. But there are scores of Boston firefighters whose shifts have been covered by others for weeks or months at a time, with no record they have ever reciprocated and worked off the debt.(By Callum Borchers, Gal Tziperman Lotan, and Walter V. Robinson, Globe Correspondents)

President Hosni Mubarak of Egypt struggled to maintain a tenuous hold on power yesterday as the police withdrew from the major cities and the military did nothing to hold back tens of thousands of demonstrators defying a curfew to call for an end to his nearly 30 years of authoritarian rule.(By David D. Kirkpatrick, New York Times)